UV will help for sure but no its also never going to be able to make a tank ich free. The biggest problem is contact time. Ich has to come into contact with the UV to kill it and most ich will never leave the display, travel down the overflow and through the UV. Ich doesn't swim enough. It generally swims very little looking for a host and attaches to whatever it finds. In a closed system its not very hard to find a host. In most cases (where the ich is bad enough) we are talking about thousands and thousands of parasites swimming around and only a fraction of that end up finding a host but thats all thats needed to cover a fish in ich. Basically the percentage finding a host is very low but it doesn't matter because its a closed system which gives ich a huge advantage when in large numbers. Thats also the reason flow has nothing to do with preventing ich. If only it were that easy! Your not going to stop hundreds or thousands of parasites from attaching to a fish because they are "blowing" around. Sure this may stop some but imagine a thousand little grains of salt floating around in your tank with strong flow...they are still going to be hitting your fish constantly.
While we are on the subject...Cleaner wrasse, cleaner shrimp and other "cleaners" generally do nothing to stop ich either. Its cool to see a fish get cleaned but what you are seeing is the cleaner eating dead skin/scales or dead parasites that have let go of the host. Ich burrows under the skin (thats the white spots you see) and for the most part cannot be touched by "cleaners". A fishes slime coat will also unfortunately protect the parasites.
Ich is a tough one to deal with sometimes but IMO should not kill fish unless it gets out of hand. I have lost fish of course to ich over the years but never recently and I have stopped with meds. Maybe its just luck but I don't feel thats the case. Choosing healthy fish and keeping them very well fed (I swear by the Tropic Marin Vitamins) and in very good water conditions seems to give the fish a fighting chance and least amount of stress. I have seen a connection in my tanks between nitrates over 20 and ich. Again, could be a coincidence but my FOWLR used to get ich every time the nitrates went over 20 PPM. I feel strongly that even in a fish only tank nitrates should be kept down to a reasonable level or you have too many fish. I have kept large puffers, groupers, lions, ect. and know you can keep nitrates low with good husbandry and equipment.
But anyways that would be another rant
